A. Field of the Invention
The present invention relates generally to the field of bacteriology. In certain aspects, the present invention is directed to modified photoautotrophic bacteria with overexpressed, down-regulated, introduced, deleted or modified genes of interest to produce a desired product. The desired product can be processed into a biofuel, bioplastic, animal feed additive, nutraceutical, food additive, fertilizer, etc.
B. Background
Two challenges facing the world today include the ongoing pollution of the environment with carbon dioxide which contributes to global warming and the increasing consumption of the world's natural energy resources such as fossil fuels. A problematic cycle exists where the increase in fossil fuel consumption correlates with an increase in carbon dioxide air pollution.
For instance, it has been estimated that the United States produces 1.7 billion tons of carbon dioxide annually from the combustion of fossil fuels (see U.S. Publication No. 2002/0072109). This pales in comparison to the global production of carbon dioxide from fossil fuel consumption which is estimated to be between 7-8 billion tons/year (Marland et al. 2006). An increase in carbon dioxide air pollution can lead to an increase in global warming and in turn can increase the frequency and intensity of extreme weather events, such as floods, droughts, heat waves, hurricanes, tornadoes, etc. Other consequences of global warming can include changes in agricultural yields, species extinctions, and increases in the ranges of disease vectors.
Methods for carbon dioxide remediation have been suggested. For instance, U.S. Publication No. 2002/0072109 discloses an on-site biological sequestration system that can decrease the concentration of carbon-containing compounds in the emissions of fossil-fuel powered power generation units. The system uses photosynthetic microbes such as algae and cyanobacteria which are attached to a growth surface arranged in a containment chamber that is lit by solar photons. The cyanobacteria uptake and utilize the carbon dioxide produced by the fossil-fuel powered power generation units.
As for the second challenge, global energy demand continues to increase which places a higher demand on the non-renewable fossil fuel energy supplies. Alternative sources for energy have recently been developed. For instance, agricultural products such as corn, soybeans, flaxseed, rapeseed, sugar cane, and palm oil are currently being grown for use in biofuel production. Biodegradable by-products from industries such as the agriculture, housing, and forestry industries can also be used to produce bioenergy. For example, straw, timber, manure, rice, husks, sewage, biodegradable waste and food leftovers can be converted into biogas through anaerobic digestion. However, plant productivity has a low yield of conversion of solar energy to biomass and biofuels, due to limitations in CO2 diffusion and sequestration, growing season, and solar energy collection over the course of the year. A higher efficiency of solar energy conversion is achieved by algae and cyanobacteria.
Methods for using living organisms to produce ethanol have also been described. For instance, U.S. Pat. No. 4,242,455 to Muller et al. describes a continuous process in which an aqueous slurry of carbohydrate polymer particles, such as starch granules and/or cellulose chips, fibers, etc., are acidified with a strong inorganic acid to form a fermentable sugar. The fermentable sugar is then fermented to ethanol with at least two strains of Saccharomyces. U.S. Pat. No. 4,350,765 to Chibata et al. describes a method of producing ethanol in a high concentration by using an immobilized Saccharomyces or Zymomonas and a nutrient culture broth containing a fermentative sugar. U.S. Pat. No. 4,413,058 to Arcuri et al. describes a strain of Zymomonas mobilis which is used to produce ethanol by placing the microorganism in a continuous reactor column and passing a stream of aqueous sugar through said column.
PCT Application WO/88/09379 to Hartley et al. describes the use of facultative anaerobic thermophilic bacterial strains which produce ethanol by fermenting a wide range of sugars, including cellobiose and pentoses. These bacterial strains contain a mutation in lactate dehydrogenase. As a result, these strains which would normally produce lactate under anaerobic conditions, produce ethanol instead.
U.S. Publication 2002/0042111 discloses a genetically modified cyanobacterium that can be used to produce ethanol. The cyanobacterium includes a construct comprising DNA fragments encoding pyruvate decarboxylase (pdc) and alcohol dehydrogenase (adh) enzymes obtained from the Zymomonas mobilis plasmid pLOI295.